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Study On Beam Characteristics Of High Power Transverse F Low CO2 Laser And Its Influence On Processing Quality

Posted on:2009-01-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:R T ZhongFull Text:PDF
GTID:1118360275971077Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Beam characteristics of high power CO2 laser is an important factor to determine the laser processing quality. In the dissertation, based on high power transverse CO2 laser and its processing system, beam characteristics(including energe,mode and focus) of high power CO2 laser and their influences on penetration welding and surface modification are studied systematically.(1) Output intensity distribution of continuous transverse CO2 laser with plane-cone cavity is studied and theoretical model of modes in the cavity is established. Furthermore, output beam characteristics of plane-concave cavity and plane-cone cavity are compared. Corresponding beam divergence angle of them are 2.6mrad and 2.1mrad respectively. When the maladjustment of the output mirror is 1.4', absence ratios of the output beam are 16% and 8% respectively. And when the reflector has 1.4'maladjustment, absence ratios of the output beam are 20% and 5% respectively. So plane-cone cavity has high anti-maladjustment stability. Concept of time-beam-quality and three evaluation parameters of transverse CO2 laser beam are presented , including ratio of power fluctuant frequency and power fluctuate ( fΔP/P ), ratio of beam diameter changed frequency and beam diameter fluctuate ( fΔD/D ),ratio of beam center changed frequency and beam center fluctuate ( fΔC/C ). It can be inferred that time-beam-quality is better and beam stability is higher as the three parameters larger.(2) Theoretical model of intensity distribution of integral-focusing mirror is established and influence of power distribution in the focus on surface modification quality is studied. By adjusting side length and mirror numbers, beam with convex, uniform or concave intensity distribution can be obtained. hardness zone of beam with concave intensity distribution is broader, more even and bottom of it is nearly smooth, which is favorable for laser surface modification. In addition, influences of plane-convex transmission mirror and paraboloid reflection focusing mirror on penetration welding are compared. When the incident beam is vertical, compared with plane-convex mirror, laser welding penetration of paraboloid focusing mirror is 15% larger and the corresponding welding width is 10% smaller. But when the deflexion is 0.6mm, welding penetration of it is smaller than the corresponding plane-convex mirror. (3) To study the influence of beam characteristics of high power CO2 laser on welding quality, welding experiment of material 316L, Q235A , powder metallurgy (PM)and sandwich material has been done. And relationships between laser power P (kW), welding speed v (m/min), focusing length f (mm), M2 factor and welding quality have been established,welding penetration (mm) : ,welding strength (Mpa), . Welding defects of laser welding sandwich material usually exhibit as large numbers of air hole and quite excessive copper, which leads to the welding strength decrease. Welding half penetration from the obverse side and then welding another half from the reverse side, or increase welding speed can decrease air hole in the welding zone.(4) The influences on cladding quality of multi-modes continuous/pulse beam have been studied experimentally, With pulse laser beam, cladding layer crackings on areoengine blade can be solved. Compared with continuous laser beam, cladding layer under pulse laser has a 4%-6% increasement of hardness but 9%-18% decreasement of duty rate and 50% decreasement of heat-affected zone. The influences on laser surface phase transformation quenching quality of beam form have been analysed,the biggest surface hardness can be achieved When the triangle beam is used, the biggest width of hardness zone can be achieved when the rectangular beam is used, the biggest depth of hardness zone can be achieved when the circle beam is used.
Keywords/Search Tags:beam characteristics of transverse flow CO2 laser, cone mirror cavity, time- quality of beam, laser deep penetration welding, powder metallurgy material, sandwich material, continuous/pulse laser cladding
PDF Full Text Request
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